Experiments on the Eleven-Year Changes of Cosmic-Ray Intensity Using a Space Probe

Experiments in which cosmic radiation detectors were carried into space by Explorer VI and Pioneer V proved that any mechanism changing the cosmic-ray intensity over 11 years is centered about the sun. The scale size is > 1 astronomical unit for the volume of space in which the cosmic-ray intensity is reduced at this period of the solar activity cycle. Cosmic-ray flux was approximately constant from inside the terrestrial field far into the interplanetary medium. Therefore the 11-year depression of cosmic-ray intensity is not geocentric. A radial omnidirection intensity gradient of -(15 plus or minus 20)%/A was measured near the orbit of the earth and in the direction of the sun. This gradient showed that any electromagnetic-modulating mechanism required to account for the 11-year intensity variation is located principally outside the orbit of the earth. (M.C.G.)